The present invention is generally directed to fuel cell components, and to solid oxide fuel cells in particular.
Fuel cells are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. Electrolyzer cells are electrochemical devices which can use electrical energy to reduce a given material, such as water, to generate a fuel, such as hydrogen. The fuel and electrolyzer cells may comprise reversible cells which operate in both fuel cell and electrolysis mode.
In a high temperature fuel cell system, such as a solid oxide fuel cell (SOFC) system, an oxidizing flow is passed through the cathode side of the fuel cell while a fuel flow is passed through the anode side of the fuel cell. The oxidizing flow is typically air, while the fuel flow can be a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, or methanol. The fuel cell, operating at a typical temperature between 750° C. and 950° C., enables the transport of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ion combines with either free hydrogen or hydrogen in a hydrocarbon molecule to form water vapor and/or with carbon monoxide to form carbon dioxide. The excess electrons from the negatively charged ion are routed back to the cathode side of the fuel cell through an electrical circuit completed between anode and cathode, resulting in an electrical current flow through the circuit. A solid oxide reversible fuel cell (SORFC) system generates electrical energy and reactant product (i.e., oxidized fuel) from fuel and oxidizer in a fuel cell or discharge mode and generates the fuel and oxidant using electrical energy in an electrolysis or charge mode.
Fuel cell stacks are frequently built from a multiplicity of cells in the form of planar elements, tubes, or other geometries. Fuel cell stacks, particularly those with planar geometry, often use seals between electrolyte and interconnect surfaces to contain fuel and air at various locations within the stack. As shown in FIG. 1, in fuel cell stacks that are internally manifolded for fuel (i.e., in which fuel is provided through fuel riser openings in SOFCs and interconnects in the stack) electrolyte crack formation has been observed at ring seals initiated by cell electrolyte corrosion. A ring seal is a seal that surrounds the fuel inlet and fuel outlet riser openings between the cathode (i.e., air) side of a given SOFC and an air side of an adjacent interconnect (also known as a gas separator plate). This corrosion in conjunction with stresses which occur during operation lead to cracks, cell cracking and catastrophic failure at elevated temperatures (e.g., after 2 hours at 900 C) as shown in FIG. 2.